The present invention relates to a lifting appliance having a telescopic column and a lifting means mounting which is supported by said column and which, during telescopic extension and retraction of the column, can be set in optional vertical positions.
Such lifting appliances are frequently used in care of the sick and aged as patient lifting devices which are usually mounted on an undercarriage to enable the patient carried by the lifting appliance to be moved between different locations. The patient lifting appliance is, in a prior art design, to be compared to a crane where the lifting means mounting is rigidly attached to the displaceable part of the telescopic column, thereby following the vertical motions of the displaceable part. In other prior art lifting appliances, use is made of an unextendable column provided with a carriage serving as the lifting means mounting, said carriage being reciprocable, by means of a driving motor, in the longitudinal direction of the column. The last-mentioned type of prior art appliances suffers from the drawback that the length of the column must be sufficient for the entire desired hoisting motion of the carriage, whereas a disadvantage of the first-mentioned type using a telescopic column is that the stroke of the telescopic column corresponds to the maximum lifting distance of the lifting means, which results in, inter alia, a considerable overall height also in the completely retracted state. To eliminate these drawbacks, DE-A-3,602,105 and EP-A-0,267,888 suggest a lifting appliance, especially for a patient lifting device, comprising a column having two telescopically cooperating column elements and a driving motor for adjusting the length of said column and having a lifting means mounting consisting of a carriage which is movable to optional positions along one column element by means of a belt attached to said carriage and running over a deflecting roller mounted on one column element, to a belt attachment on the other column element. This prior art design gives the lifting appliance a small overall height and great vertical adjustability of the lifting means mounting. Yet there are some drawbacks with respect to safety in operating the lifting appliance. Thus, it is necessary to arrest the telescopic motion of the column in case of defects in the power train, or in case the carriage or a lifting means connected therewith should be stopped by some object in its downward movement.